Disordered fibrin turnover and extravascular fibrin deposition have been implicated in the pathogenesis of lung injury and repair and lung cancer. Lung epithelial cells contribute to remodeling of extravascular fibrin by elaboration of urokinase (uPA), the urokinase receptor (uPAR) and plasminogen activator inhibitor-1 (PAl-1). Abnormal expression of these molecules in lung injury and neoplasia disrupts local fibrin turnover, potentiates local inflammation, and promotes organization of transitional fibrin with eventual fibrosis. We recently found that uPA induces expression of uPAR by lung epithelial cells. We now demonstrate that exogenous uPA also induces uPA and PAI-1 expression by these cells. These studies clearly show that lung epithelial cells regulate the uPA-uPAR-PAI-1 system by novel pathways about which little is currently understood. Our preliminary data show that posttranscriptional regulation contributes to uPA-mediated autoinduction as well as that of uPAR and PAI-1. Our central hypothesis is that novel pathways by which uPA regulates its own expression as well as that of uPAR and PAI-1 by lung epithelial cells are crucial in the pathogenesis of acute lung injury, its repair and lung cancer. Our objective is to elucidate the regulatory mechanisms by which uPA induces expression of these molecules. We will accomplish the objective in four specific aims. In Aim 1, we will determine if uPA induces epithelial cell uPAR at both transcriptional or posttranscriptional levels and define the responsible mechanisms. In Aim 2, we will determine the mechanism by which a-thrombin blocks uPA-mediated uPAR induction. In Aims 3 and 4, we will determine the mechanisms by which uPA induces its own expression as well as that of PAl-1, respectively, in lung epithelial cells. We will use a wide range of molecular, immunohistochemical, protein purification, and cell culture techniques with which we are experienced to complete the proposed work. These studies will increase our understanding of novel mechanisms by which the lung epithelium regulates the uPA-uPAR-PAI-1 system. This information could hasten the development of new, mechanism-based interventions for lung disorders, including acute lung injury or lung neoplasia.